US20160060413A1 - Molded body of composite resin foam - Google Patents

Molded body of composite resin foam Download PDF

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Publication number
US20160060413A1
US20160060413A1 US14/778,767 US201414778767A US2016060413A1 US 20160060413 A1 US20160060413 A1 US 20160060413A1 US 201414778767 A US201414778767 A US 201414778767A US 2016060413 A1 US2016060413 A1 US 2016060413A1
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Prior art keywords
molded article
expanded molded
composite resin
particles
expanded
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US14/778,767
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Inventor
Masahiko Ozawa
Akira Isayama
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Sekisui Kasei Co Ltd
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Sekisui Plastics Co Ltd
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Assigned to SEKISUI PLASTICS CO., LTD. reassignment SEKISUI PLASTICS CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ISAYAMA, AKIRA, OZAWA, MASAHIKO
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/0061—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof characterized by the use of several polymeric components
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
    • C08J9/12—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a physical blowing agent
    • C08J9/14—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a physical blowing agent organic
    • C08J9/141—Hydrocarbons
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/16—Making expandable particles
    • C08J9/18—Making expandable particles by impregnating polymer particles with the blowing agent
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/16—Making expandable particles
    • C08J9/20—Making expandable particles by suspension polymerisation in the presence of the blowing agent
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/22—After-treatment of expandable particles; Forming foamed products
    • C08J9/228—Forming foamed products
    • C08J9/232—Forming foamed products by sintering expandable particles
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2201/00—Foams characterised by the foaming process
    • C08J2201/02—Foams characterised by the foaming process characterised by mechanical pre- or post-treatments
    • C08J2201/034—Post-expanding of foam beads or sheets
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2203/00—Foams characterized by the expanding agent
    • C08J2203/14—Saturated hydrocarbons, e.g. butane; Unspecified hydrocarbons
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2325/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring; Derivatives of such polymers
    • C08J2325/02—Homopolymers or copolymers of hydrocarbons
    • C08J2325/04—Homopolymers or copolymers of styrene
    • C08J2325/06—Polystyrene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2423/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2423/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C08J2423/04—Homopolymers or copolymers of ethene
    • C08J2423/08—Copolymers of ethene

Definitions

  • the present invention relates to a molded body of composite resin foam (composite resin expanded molded article). More specifically, the present invention relates to a composite resin expanded molded article having superior slow-burning properties and thermal resistance.
  • expanded molded articles of a polyethylene-based resin have high elasticity, and superior oil resistance and impact resistance, they have the disadvantages of low rigidity and weak compression strength.
  • expanded molded articles of a polystyrene-based resin although having superior rigidity, have the disadvantage of being brittle.
  • expanded molded articles of a composite resin of a polyethylene-based resin and a polystyrene-based resin have been suggested, and are widely utilized as cushioning materials for packaging, heat insulation materials for building materials, structural members for vehicles, and the like.
  • Patent Document 1 discloses composite resin expanded particles prepared from 20 to 50 parts by mass of an olefin-based resin component and 80 to 50 parts by mass of a styrene-based resin component (total of both components is 100 parts by mass), wherein 1 to 15% by mass of a halogen-based flame retardant that includes a secondary or tertiary halide and that has a 50% decomposition temperature of 290 to 350° C. has been formulated, and the content of aliphatic hydrocarbons having 3 to 6 carbons is less than 0.1% by mass (includes 0).
  • Patent Document 2 discloses carbon-containing styrene-modified polyethylene-based resin particles and expandable resin particles comprising: 120 to 400 parts by weight of a styrene-based resin with respect to 100 parts by weight of a carbon-containing ethylene-vinyl acetate copolymer having a specific polymerization ratio and degree of crystallinity; and 1 to 8 parts by weight of a halogen-based flame retardant with respect to 100 parts by weight of the resin components, production methods thereof, pre-expanded particles, and an expanded molded article.
  • Patent Document 1 Japanese Unexamined Patent Application, First Publication No. 2012-72225
  • Patent Document 2 Japanese Unexamined Patent Application, First Publication No. 2006-257150
  • the composite resin expanded particles and composite resin particles disclosed in the aforementioned Patent Documents 1 and 2 have superior flame retardancy since they include a flame retardant while, on the other hand, they have the problem of thermal resistance deteriorates since they include a flame retardant.
  • the present invention has the object of providing a composite resin expanded molded article having superior slow-burning properties and thermal resistance.
  • the inventors of the present invention as a result of earnest research in order to achieve the aforementioned object have expectedly found that, by making the average cell diameter and the average cell membrane thickness specific ranges in a composite resin expanded molded article comprising an ethylene-vinyl acetate copolymer and a polystyrene-based resin in a specific ratio, a composite resin expanded molded article having superior slow-burning properties and thermal resistance can be obtained even when no flame retardant is included, thus leading to completion of the present invention.
  • a composite resin expanded molded article comprising: 100 parts by mass of an ethylene-vinyl acetate copolymer; and 100 to 400 parts by mass of a polystyrene-based resin, wherein the composite resin expanded molded article has an average cell diameter D of 100 to 500 ⁇ m and an average cell membrane thickness T of 1 to 5 ⁇ m is provided.
  • a composite resin expanded molded article having superior slow-burning properties and thermal resistance can be provided.
  • the composite resin expanded molded article of the present invention further exhibits the aforementioned effect when any one of the following conditions is satisfied:
  • the composite resin expanded molded article does not include a flame retardant; (2) the average cell diameter D and the average cell membrane thickness T satisfy the relationship of 200 ⁇ D ⁇ T ⁇ 1,100; and (3) the content of aliphatic hydrocarbons having 3 to 6 carbons in the composite resin expanded molded article is 0.5% by mass or less.
  • the composite resin expanded molded article of the present invention exhibits superior slow-burning properties and thermal resistance even when a flame retardant is not included.
  • FIG. 1( a ) is a SEM image showing the average cell membrane thickness of the composite resin expanded molded article of Example 1
  • FIG. 1( b ) is a SEM image showing the average cell diameter of the composite resin expanded molded article of Example 1.
  • FIG. 2( a ) is a SEM image showing the average cell membrane thickness of the composite resin expanded molded article of Example 2
  • FIG. 2( b ) is a SEM image showing the average cell diameter of the composite resin expanded molded article of Example 2.
  • FIG. 3( a ) is a SEM image showing the average cell membrane thickness of the composite resin expanded molded article of Comparative Example 2
  • FIG. 3( b ) is a SEM image showing the average cell diameter of the composite resin expanded molded article of Comparative Example 2.
  • the composite resin expanded molded article of the present invention (hereinafter, also referred to as “expanded molded article”) is characterized by being a composite resin expanded molded article comprising: 100 parts by mass of an ethylene-vinyl acetate copolymer; and 100 to 400 parts by mass of a polystyrene-based resin, wherein the composite resin expanded molded article has an average cell diameter D of 100 to 500 ⁇ m and an average cell membrane thickness T of 1 to 5 ⁇ m.
  • the inventors focused on the average cell diameter and the average cell membrane thickness of a composite resin expanded molded article not including a flame retardant in order to suppress deterioration in thermal resistance by the addition of a flame retardant, and upon exploration of the relationship with the slow-burning properties thereof, unexpectedly found the fact that if the average cell diameter and the average cell membrane thickness are within specific ranges, slow-burning properties equivalent to or exceeding a composite resin expanded molded article including a flame retardant can be obtained, and deterioration in thermal resistance can be suppressed from not including a flame retardant.
  • Patent Document 1 discloses that the preferable average cell diameter of the composite resin expanded particles is 50 to 500 ⁇ m and that if the average cell diameter exceeds 500 ⁇ m, there is the possibility of deterioration in strength and worsening of flame retardancy in the obtained expanded molded article. However, there is nothing disclosed therein about the average cell membrane thickness of the composite resin expanded particles and the relationship between this and the average cell diameter.
  • Patent Document 2 does not disclose about the average cell diameter and the average cell membrane thickness of the pre-expanded particles, and the relationship between these.
  • polystyrene-based resin constituting the expanded molded article there are no particular limitations on the polystyrene-based resin constituting the expanded molded article so long as such is a resin having a styrene-based monomer as the main component, and styrene or a styrene derivative alone or as a copolymer can be mentioned.
  • styrene derivatives ⁇ -methylstyrene, vinyl toluene, chlorostyrene, ethylstyrene, isopropylstyrene, dimethylstyrene, bromostyrene, and the like can be mentioned. These styrene-based monomers may be used alone or may be combined.
  • the polystyrene-based resin may be a resin that is combined with a vinyl-based monomer copolymerizable with a styrene-based monomer.
  • vinyl-based monomers for example, multifunctional monomers such as divinylbenzenes such as o-divinylbenzene, m-divinylbenzene, and p-divinylbenzene, and alkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate and polyethylene glycol di(meth)acrylate; (meth)acrylonitrile; methyl (meth)acrylate; butyl (meth)acrylate; and the like can be mentioned.
  • divinylbenzenes such as o-divinylbenzene, m-divinylbenzene, and p-divinylbenzene
  • alkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate and polyethylene glycol di(meth)acrylate; (meth)acrylonitrile; methyl (meth)acrylate; butyl (meth)acrylate; and the like can be mentioned.
  • multifunctional monomers are preferable, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylates in which n is 4 to 16, and divinylbenzenes are more preferable, and divinylbenzenes and ethylene glycol di(meth)acrylate are particularly preferable.
  • the combined monomers may be used alone or may be combined.
  • the content thereof is set so that the styrene-based monomer is an amount so as to become the main component (for example, 50% by mass or more).
  • (meth)acryl means “acryl” or “methacryl”.
  • ethylene-vinyl acetate copolymer constituting the expanded molded article there are particularly no limitations on the mass ratio and the like thereof so long as such is a copolymer of vinyl acetate and ethylene.
  • copolymers of 3.0 to 7.0% by mass of vinyl acetate and 93.0 to 97.0% by mass of ethylene can be mentioned.
  • a copolymer of 4.0% by mass of vinyl acetate and 96.0% by mass of ethylene as used in the examples can be mentioned.
  • the content of vinyl acetate may be appropriately selected by the target properties of the expanded molded article.
  • the vinyl acetate in the aforementioned ethylene-vinyl acetate copolymer is, for example, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, and 7.0% by mass.
  • the number-average molecular weight (M n ) of the ethylene-vinyl acetate copolymer is about 30 ⁇ 10 3 to 60 ⁇ 10 3
  • the weight-average molecular weight (M W ) of the ethylene-vinyl acetate copolymer is about 200 ⁇ 10 3 to 300 ⁇ 10 3
  • the Z-average molecular weight (M Z ) of the ethylene-vinyl acetate copolymer is about 600 ⁇ 10 3 to 1,000 ⁇ 10 3 .
  • the ratio (M W /M n ) of the weight-average molecular weight (M W ) to the number-average molecular weight (M n ) is about 4.5 to 6.5.
  • the number-average molecular weight (M n ) of the aforementioned copolymer is, for example, 30 ⁇ 10 3 , 35 ⁇ 10 3 , 40 ⁇ 10 3 , 45 ⁇ 10 3 , 50 ⁇ 10 3 , 55 ⁇ 10 3 , and 60 ⁇ 10 3 .
  • the weight-average molecular weight (M W ) of the aforementioned copolymer is, for example, 200 ⁇ 10 3 , 225 ⁇ 10 3 , 250 ⁇ 10 3 , 275 ⁇ 10 3 , and 300 ⁇ 10 3 .
  • the Z-average molecular weight (M Z ) of the aforementioned copolymer is, for example, 600 ⁇ 10 3 , 700 ⁇ 10 3 , 800 ⁇ 10 3 , 900 ⁇ 10 3 , and 1,000 ⁇ 10 3 .
  • the aforementioned ratio (M W /M n ) is, for example, 4.5, 5.0, 5.5, 6.0, and 6.5.
  • the polystyrene-based resin is 100 to 400 parts by mass with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer.
  • polystyrene-based resin is less than 100 parts by mass, the polystyrene-based resin is insufficient, and thus desired expandabilty may not be obtainable, and the rigidity of the expanded molded article obtained by secondary expansion of the pre-expanded particles may deteriorate.
  • the polystyrene-based resin exceeds 400 parts by mass, the slow-burning properties and the thermal resistance of the expanded molded article obtained by secondary expansion of the pre-expanded particles may deteriorate.
  • Such polystyrene-based resin with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer is, for example, 100, 150, 200, 250, 300, 350, and 400 parts by mass.
  • the polystyrene-based resin is more preferably 100 to 300 parts by mass, and further preferably 100 to 250 parts by mass, with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer.
  • the ratio of the raw material resin and monomer is roughly equal to the ratio thereof in the expanded particles and the expanded molded article.
  • the expanded molded article of the present invention has an average cell diameter D of 100 to 500 ⁇ m.
  • Average cell diameter D means the average cell diameter D ( ⁇ m) of expanded particles in the expanded molded article measured in accordance with the test method of ASTM D2842-69, and the specific measurement method thereof is explained in the “Examples” section.
  • the average cell diameter D is less than 100 ⁇ m, fusion of the expanded molded article obtained by secondary expansion of pre-expanded particles deteriorates, and thus there is the possibility that this leads to deterioration of rigidity.
  • the average cell diameter D exceeds 500 ⁇ m, the slow-burning properties of the expanded molding article may deteriorate.
  • Such average cell diameter D is, for example, 100, 150, 200, 250, 300, 350, 400, 450, and 500 ⁇ m.
  • a preferable range of the average cell diameter D is from 100 to 400 ⁇ m, and a more preferable range is from 150 to 350 ⁇ m.
  • the expanded molded article of the present invention has an average cell membrane thickness T of 1 to 5 ⁇ m.
  • the expanded molded article is divided into two in the thickness direction, and means the average value of the thickness ( ⁇ m) in 5 arbitrarily selected expanded particles from the slice of the expanded molded article divided into two.
  • the specific measurement method thereof is explained in the “Examples” section.
  • the average cell membrane thickness T is less than 1 ⁇ m, there is the possibility that this leads to deterioration of the rigidity of the expanded molded article obtained by secondary expansion of pre-expanded particles. On the other hand, if the average cell membrane thickness T exceeds 5 ⁇ m, the slow-burning properties of the expanded molded article may worsen.
  • Such average cell membrane thickness T is, for example, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 p.m.
  • a preferable range of the average cell membrane thickness T is from 1.0 to 4.0 ⁇ m, and a more preferable range is from 1.4 to 3.5 ⁇ m.
  • the average cell diameter D and the average cell membrane thickness T satisfy the relationship of 200 ⁇ D ⁇ T ⁇ 1,100.
  • (D ⁇ T) is less than 200, there is the possibility that this leads to deterioration of the rigidity of the expanded molded article obtained by secondary expansion of pre-expanded particles.
  • (D ⁇ T) exceeds 1,100, the slow-burning properties of the expanded molded article may worsen.
  • Such (D ⁇ T) is, for example, 200, 300, 400, 500, 600, 700, 800, 900, 1,000, and 1,100.
  • a more preferable range of (D ⁇ T) is 200 to 1,000.
  • the content of aliphatic hydrocarbons having 3 to 6 carbons in the composite resin expanded molded article is preferably 0.5% by mass or less.
  • the hydrocarbons having 3 to 6 carbons are derived from the blowing agent, and if the content in the expanded molded article thereof exceeds 0.5% by mass, the slow-burning properties and the rigidity of the expanded molded article may worsen.
  • Such content of aliphatic hydrocarbons is, for example, 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, and 0.5% by mass.
  • the minimum thereof is preferably 0% by mass, and a more preferable content range is from 0 to 0.3% by mass.
  • the expanded molded article of the present invention preferably has a density of 0.025 to 0.05 g/cm 3 .
  • the density exceeds 0.05 g/cm 3 , the lightweight properties of the expanded molded article may deteriorate.
  • the density is less than 0.025 g/cm 3 , by shrinkage occurring in the obtained expanded molded article, the appearance may not be good and also, the thermal resistance and the slow-burning properties of the expanded molded article may deteriorate.
  • Such density of the expanded molded article is, for example, 0.025, 0.030, 0.035, 0.040, 0.045, and 0.050 g/cm 3 .
  • a more preferable density range is from 0.025 to 0.035 g/cm 3 , and a further preferable range is from 0.028 to 0.035 g/cm 3 .
  • the expansion ratio of the expanded molded article is represented by the inverse of the density of the expanded molded article, and for the aforementioned preferable density range becomes 20 to 40.
  • the expanded molded article of the present invention has superior slow-burning properties and thermal resistance while not including a flame retardant.
  • the slow-burning properties as explained in the “Examples” section, can be measured in accordance with the method of United States Federal Motor Vehicle Safety Standard FMVSS 302 “Flammability of Interior Materials”.
  • a burning speed of 100 mm/min or less, or 80 mm/min or less is the pass reference.
  • the expanded molded article of the present invention has slow-burning properties equivalent to or exceeding those of an expanded molded article including a flame retardant.
  • the thermal resistance can be evaluated with the rate of dimensional change on heating thereof as the indicator.
  • the rate of dimensional change on heating can be measured in accordance with the B method described in JIS K6767: 1999 “Cellular Plastics-Polyethylene-Methods of Test”, and the specific measurement method thereof is explained in the “Examples” section.
  • the expanded molded article of the present invention preferably has a rate of dimensional change on heating of 1.0% or less.
  • the rate of dimensional change on heating is more preferably 0.9% or less, and further preferably 0.7% or less.
  • the expanded molded article of the present invention can be produced by obtaining expandable particles by impregnating a blowing agent into the aforementioned composite resin particles, obtaining expanded particles by pre- (primary) expanding the obtained expandable particles, and expansion molding the obtained expanded particles.
  • seed polymerization methods can obtain composite resin particles by absorbing a monomer mixture into seed particles and carrying out polymerization of the monomer mixture after absorption or while absorbing.
  • expandable resin particles can be obtained by impregnating a below-mentioned blowing agent into composite resin particles after polymerization or while polymerizing.
  • additives are included in the composite resin particles, these may be added at the time of polymerization of the monomer mixture or may be impregnated into the composite resin particles after the completion of polymerization.
  • a monomer mixture including a monomer of a styrene-based resin (hereinafter, also referred to as “styrene monomer”) is absorbed into the ethylene-vinyl acetate copolymer particles as seed particles in an aqueous medium, and the composite resin particles are obtained by carrying out polymerization of the monomer mixture after absorption or while absorbing.
  • the additives may be added to the monomer mixture or the aqueous medium, or may be contained in the seed particles.
  • aqueous medium water, and a mixed medium of water and a water-soluble medium (for example, a lower alcohol such as methyl alcohol or ethyl alcohol) can be mentioned.
  • a water-soluble medium for example, a lower alcohol such as methyl alcohol or ethyl alcohol
  • a known dispersant may be used in the aqueous medium in order to stabilize the droplets of monomer mixture and dispersion properties of the seed particles.
  • organic-based dispersants such as partially-saponified polyvinyl alcohol, polyacrylic acid salts, polyvinyl pyrrolidone, carboxymethyl cellulose, and methyl cellulose
  • inorganic-based dispersants such as magnesium pyrophosphate, calcium pyrophosphate, calcium phosphate, calcium carbonate, magnesium phosphate, magnesium carbonate, and magnesium oxide can be mentioned.
  • inorganic-based dispersants are preferable since it is possible to maintain a more stable dispersed state.
  • an inorganic-based dispersant it is preferable to use in combination with a surfactant.
  • a surfactant for example, sodium dodecyl benzenesulfonate, sodium ⁇ -olefinsulfonate, and the like can be mentioned.
  • Polymerization of the monomer mixture can be carried out, for example, by heating at 60 to 150° C. for 2 to 40 hours.
  • the polymerization can be carried out after the monomer mixture has been absorbed into the seed particles or while absorbing the monomer mixture into the seed particles.
  • the amounts of the monomer and the resin are roughly equal.
  • the monomer mixture is normally polymerized in the presence of a polymerization initiator.
  • the polymerization initiator is normally impregnated simultaneously into the seed particles with the monomer mixture.
  • the polymerization initiator is not particularly limited so long as it has been conventionally used in the polymerization of styrene-based monomers.
  • organic peroxides such as benzoyl peroxide, t-butylperoxy benzoate, t-butylperoxy pivalate, t-butylperoxy-2-ethylhexyl monocarbonate, t-butylperoxy isopropyl carbonate, t-butylperoxyacetate, 2,2-t-butylperoxybutane, t-butylperoxy-3,3,5-trimethyl hexanoate, di-t-butylperoxy hexahydroterephthalate, 2,5-dimethyl-2,5-bis(benzoylperoxy) hexane, and dicumyl peroxide can be mentioned.
  • These polymerization initiators may be used alone or by combining two or more thereof.
  • the used amount of polymerization initiator is, for example
  • seed particles can be produced by a publicly-known method.
  • suspension polymerization methods and methods of, after melting and kneading the raw material resin in an extruder, extruding as strand shapes and cutting to desired particle diameters, can be mentioned.
  • the particle diameter of the seed particles can be appropriately adjusted according to the average particle diameter and the like of the composite resin particle to be produced. For example, when composite resin particles having an average particle diameter of 1.5 mm are produced, preferably seed particles having an average particle diameter of about 0.8 to 1.0 mm are used (about 70 to 75 mg per 100 particles).
  • the monomer mixture may include additives such as plasticizers, lubricants, binding inhibitors, fusion accelerators, cell regulators, antistatic agents, spreaders, fillers, crosslinking agents, and coloring agents.
  • additives such as plasticizers, lubricants, binding inhibitors, fusion accelerators, cell regulators, antistatic agents, spreaders, fillers, crosslinking agents, and coloring agents.
  • the additives may be included at the time of production of the composite resin.
  • plasticizers phthalic acid esters; glycerin fatty acid esters such as glycerin diacetomonolaurate, glycerin tristearate, and diacetylated glycerin monostearate; adipic acid esters like diisobutyl adipate; and the like can be mentioned.
  • paraffin wax paraffin wax, zinc stearate, and the like can be mentioned.
  • binding inhibitors calcium carbonate, silica, zinc stearate, aluminum hydroxide, ethylene bis-stearic acid amide, calcium phosphate tribasic, dimethyl silicone, and the like can be mentioned.
  • stearic acid As fusion accelerators, stearic acid, stearic acid triglycerides, hydroxystearic acid triglycerides, stearic acid sorbitan esters, polyethylene wax, and the like can be mentioned.
  • ethylene bis-stearic acid amide As cell regulators, ethylene bis-stearic acid amide, polyethylene wax, and the like can be mentioned.
  • polyoxyethylene alkylphenol ethers As antistatic agents, polyoxyethylene alkylphenol ethers, stearic acid monoglycerides, and the like can be mentioned.
  • organic peroxides such as 2,2-di-t-butyl peroxybutane, 2,2-bis(t-butylperoxy)butane, dicumyl peroxide, and 2,5-dimethyl-2,5-di-t-butyl peroxyhexane can be mentioned.
  • coloring agents carbon; chromates such as chrome yellow, zinc yellow, and barium yellow; ferrocyanides such Prussian blue; sulfides such as cadmium yellow and cadmium red; oxides such as iron black and red oxide; inorganic-based pigments such as silicates like ultramarine blue and titanium oxide; and organic-based pigments such as azo pigments such as monoazo pigments, disazo pigments, azo lakes, condensed azo pigments, and chelate azo pigments and polycyclic pigments such as phthalocyanine-based pigments, anthraquinone-based pigments, perylene-based pigments, perinone-based pigments, thioindigo-based pigments, quinacridone-based pigments, dioxazine-based pigments, isoindolinone-based pigments, and quinophthalone-based pigments can be mentioned.
  • the shape of the composite resin particles is not particularly limited, and spherical, oval, columnar, and the like can be mentioned, and among these shapes, spherical is preferable.
  • the average particle diameter thereof considering the filling properties in molding cavities and the like of the expanded particles thereafter expanded by impregnating a blowing agent, is preferably 0.5 to 2.0 mm.
  • the expandable particles are obtained by impregnating a blowing agent into the composite resin by a publicly-known method.
  • blowing agent there are no particular limitations so as long as such has been conventionally used in the expansion of polystyrene-based resins.
  • volatile blowing agents such as aliphatic hydrocarbons having 10 or less carbons such as isobutane, n-butane, n-pentane, isopentane, neopentane, and cyclopentane can be mentioned.
  • butane-based blowing agents and pentane-based blowing agents are preferable, and volatile blowing agents having pentane as the main component (for example, 50% by weight or more) are particularly preferable. It can be also expected that pentane will act as a plasticizer.
  • the content of the blowing agent in the expandable particles is normally about 8.0 to 10.0% by mass. Such content is, for example, 8.0, 8.5, 9.0, 9.5, and 10.0% by mass.
  • the expandable particles may include a blowing auxiliary agent and a plasticizer with the blowing agent.
  • aromatic organic compounds such as styrene, toluene, ethylbenzene, and xylene; cyclic aliphatic hydrocarbons such as cyclohexane and methylcyclohexane; solvents that have a boiling point of 200° C. or less at 1 atm such as ethyl acetate and butyl acetate, and plasticizers such as diisobutyl adipate, diacetylated monolaurate, and coconut oil can be mentioned.
  • the content of the blowing auxiliary agent in the expandable particles is normally about 0.1 to 1.0% by mass. Such content is, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0% by mass.
  • the expanded particles are obtained by expanding (pre-expanding) the expandable particles by a publicly-known method.
  • the expanded particles can be obtained by pre-expanding the expandable particles of the present invention to a predetermined bulk density by a publicly-known method.
  • the conditions in pre-expansion may be appropriately selected by the used resin particles, desired physical properties, and the like.
  • the stress gauge pressure
  • the temperature is about 85 to 100° C.
  • the time is about 60 to 180 seconds.
  • air may be simultaneously fed with steam according to necessity when expanding.
  • the bulk density of the expanded particles is about 0.023 to 0.05 g/cm 3 .
  • Such bulk density is, for example, 0.023, 0.025, 0.030, 0.035, 0.040, 0.045, and 0.050 g/cm 3 .
  • the expandable particles may be subjected to a warm air treatment under the conditions of a temperature lower than that at pre-expansion, for example, about 40 to 70° C., for about 0.5 to 3 hours, or the expandable particles may be pre-expanded in two stages. As the conditions thereof, the second expansion is carried out within 4 to 72 hours from the first expansion.
  • the expanded molded article is obtained by expansion molding the expanded particles by a public-known method.
  • the expanded molded article can be obtained by filling the expanded particles into the built-in molding cavity of a molding machine and then thermally-fusing the expanded particles so as to integrate while secondary expanding by heating.
  • the conditions in expansion molding may be appropriately selected by the used resin particles, desired physical properties, and the like.
  • the stress (gauge pressure) is about 0.06 MPa to 0.12 MPa and the heating time is about 15 to 60 seconds.
  • the density and other physical properties of the expanded molded article are as mentioned above.
  • the obtained expanded molded articles were measured and evaluated as follows.
  • the devices used in measurement and evaluation are one example thereof and there are no limitations so long as they have equivalent functions.
  • the bulk density of the expanded particles was measured as follows.
  • a weight (a) of about 5 g of expanded particles was weighed to two decimal places.
  • the obtained expanded particles were placed in a 500 cm 3 measuring cylinder having a minimum memory unit of 5 cm 3 .
  • a pressing tool composed of a circular resin plate having a diameter slightly smaller than the diameter of the measuring cylinder and a bar-like resin plate having a width of about 1.5 cm and a length of about 30 cm fixed upright to the center of the circular resin plate was abutted against the opening of the measuring cylinder so as to read a volume (b) of the expanded particles.
  • the average cell diameter D ( ⁇ m) of expanded particles in the expanded molded article was measured in accordance with the test method of ASTM D2842-69.
  • the photographed images were printed on A4 paper, one image per page, and two straight lines passing through the center of the expanded particle were drawn so as to be orthogonal with each other, and the length of these straight lines and the number of cells on these straight line were measured (cells contacting the straight lines were also measured).
  • the arbitrarily straight lines should be drawn such that the cells do not contact only at contact points wherever possible, if not cells contacting the straight lines should be counted in.
  • the cell diameter was calculated from the obtained cell average chord length (t) and the following equation.
  • the expanded molded article was divided into two in the thickness direction and a 300 to 3,500 times magnified image was created using a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, Model: S-3000N) for 5 arbitrarily selected expanded particles from a slice of the expanded molded article divided into two. Subsequently, using the length measurement function of the scanning electron microscope system, 5 dotted lines were arbitrarily drawn on the cell membrane and the thickness thereof was measured. The aforementioned operation was repeated for 5 points and the arithmetic average of these 5 images was used as the average cell membrane thickness T ( ⁇ m).
  • the burning speed was measured in accordance with the method of United States Federal Motor Vehicle Safety Standard FMVSS 302 “Flammability of Interior Materials”.
  • the rate of dimensional change on heating was measured according to the B method described in JIS K6767: 1999 “Cellular Plastics-Polyethylene-Methods of Test”.
  • S represents the rate of dimensional change on heating (%)
  • L1 represents the average dimensions (mm) after heating
  • L0 represents the initial average dimensions (mm).
  • rate of dimensional change on heating S (rate of shrinkage), if 1.0% or less at an absolute value was considered good and given “O” and, if exceeding 1.0%, was given “x”.
  • the density of the expanded molded article was measured in accordance with the method described in JIS A9511: 1995 “Preformed Cellular Plastics Thermal Insulation Materials”.
  • the volume V (cm 3 ) of the obtained expanded molded article and the mass thereof W (g) were measured, and the density (g/cm 3 ) of the expanded molded article was determined by the following equation.
  • Injection port temperature 110° C.
  • Ethylene-vinyl acetate copolymer resin particles manufactured by Japan Polyethylene Corporation, product name: Novatec EVA LV-115, vinyl acetate content of 4.0% by mass
  • Ethylene-vinyl acetate copolymer resin particles manufactured by Japan Polyethylene Corporation, product name: Novatec EVA LV-115, vinyl acetate content of 4.0% by mass
  • the temperature of the aqueous suspension was raised to 130° C. and stirring was continue at this temperature for 1 hour and 45 minutes to polymerize the styrene monomer (first polymerization).
  • the aqueous suspension was cooled to 90° C., and after adding 60 g of sodium dodecyl benzenesulfonate as a surfactant, 5.0 kg of a styrene monomer having 50.4 g of benzoyl peroxide and 4.0 g of t-butyl peroxybenzoate as polymerization initiators, and 98.7 g of dicumyl peroxide as a crosslinking agent dissolved therein was added dropwise thereto over 2 hours. Subsequently, 10.0 kg of a styrene monomer having dissolved therein 350 g of ethylene bis-stearic acid amide as a cell regulator was added dropwise thereto over 2 hours. Thereafter, the aqueous suspension was held at 90° C. for 1 hour.
  • the temperature of the aqueous suspension was raised to 143° C. and was held at this temperature for 2 hours to complete polymerization (second polymerization). Thereafter, the aqueous suspension was cooled to ambient temperature, and about 35 kg of composite resin particles was removed from the 100 L autoclave.
  • the used styrene monomer was 150 parts by mass with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer resin particles.
  • the expandable composite resin particles were pre-expanded to a bulk density of 0.033 g/cm 3 to obtain 2 kg of pre-expanded particles.
  • the pre-expanded particles were filled into a molding cavity having a cavity of a size of 400 ⁇ 300 ⁇ 30 mm, and this was heated by introducing 0.08 MPa of steam for 40 seconds. Thereafter, this was cooled until the surface pressure of the expanded molded article was reduced to 0.01 MPa and the expanded molded article was removed.
  • a molding cavity having a cavity of a size of 400 ⁇ 300 ⁇ 30 mm was heated by introducing 0.08 MPa of steam for 40 seconds. Thereafter, this was cooled until the surface pressure of the expanded molded article was reduced to 0.01 MPa and the expanded molded article was removed.
  • Ethylene-vinyl acetate copolymer resin particles manufactured by Japan Polyethylene Corporation, product name: Novatec EVA LV-115, vinyl acetate content of 4.0% by mass
  • Ethylene-vinyl acetate copolymer resin particles were supplied to an extruder, and heated and mixed (melt kneading), and then granulated by an under-water cutting technique and adjusted so as to become 40 mg per 100 particles to obtain 12.0 kg of ethylene-vinyl acetate copolymer resin particles (pellets).
  • the temperature of the aqueous suspension was raised to 130° C. and stirring was continue at this temperature for 1 hour and 45 minutes to polymerize the styrene monomer (first polymerization).
  • the aqueous suspension was cooled to 90° C., and after adding 60 g of sodium dodecyl benzenesulfonate as a surfactant and 6.6 kg of a styrene monomer having 58.8 g of benzoyl peroxide and 4.4 g of t-butyl peroxybenzoate as polymerization initiators, and 90 g of dicumyl peroxide as a crosslinking agent dissolved therein was added dropwise thereto over 2 hours. Subsequently, 13.4 kg of a styrene monomer having dissolved therein 350 g of ethylene bis-stearic acid amide as a cell regulator was added dropwise thereto over 2 hours. Thereafter, the aqueous suspension was held at 90° C. for 1 hour.
  • the temperature of the aqueous suspension was raised to 143° C. and was held at this temperature for 2 hours to complete polymerization (second polymerization). Thereafter, the aqueous suspension was cooled to ambient temperature, and about 35 kg of composite resin particles was removed from the 100 L autoclave.
  • the used styrene monomer was 230 parts by mass with respect to 100 parts by mass of the ethylene-vinyl acetate copolymer resin particles.
  • FIG. 1( a ) is a SEM image showing the average cell membrane thickness of the expanded molded article of Example 1
  • FIG. 1( b ) is a SEM image showing the average cell diameter of the expanded molded article of Example 1. It is shown that these are 1.5 ⁇ m and 150 ⁇ m respectively.
  • FIG. 2( a ) is a SEM image showing the average cell membrane thickness of the expanded molded article of Example 2
  • FIG. 2( b ) is a SEM image showing the average cell diameter of the expanded molded article of Example 2. It is shown that these are 3.1 ⁇ m and 292 ⁇ m respectively.
  • FIG. 3( a ) is a SEM image showing the average cell membrane thickness of the expanded molded article of Comparative Example 2
  • FIG. 3( b ) is a SEM image showing the average cell diameter of the expanded molded article of Comparative Example 2. It is shown that these are 12.9 ⁇ m and 550 ⁇ m respectively.
  • the expanded molded article of Example 1 compared to the expanded molded article of Comparative Example 2 having the same resin constitution, has a burning speed slower by 18 mm/min, and thus has slow-burning properties.

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